Not applicable.
Not applicable.
1. Field of the Invention
The invention relates to a particle detector for detecting particles of sizes of less than one micron, comprising radiation emitting means for emitting radiation at two different wavelengths along a predetermined path through a scattering volume, the radiation at one of the wavelengths lying between about 400 nm and about 500 nm, and radiation detection means for receiving and detecting the radiation scattered from the scattering volume by the presence of particles at a predetermined forward scattering angle of less than 45xc2x0 to the predetermined path of radiation.
2. Description of the Related Art including Information Disclosed under 37C.F.R. 1.97 and 1.98.
The invention also relates to a particle detecting method for detecting particles of sizes of less than one micron, comprising the steps of emitting radiation at two different wavelengths along a predetermined path through a scattering volume, one wavelength lying between about 400 nm and 500 nm, and receiving and detecting the radiation scattered from the scattering volume by the presence of particles at a predetermined forward scattering angle of less than 45xc2x0 to the predetermined path of radiation.
Such a detector and such a method are shown, for example, in GOODMAN D. S.: xe2x80x9cMETHOD FOR LOCALISING LIGHT-SCATTERED PARTICLESxe2x80x9d; IBM TECHNICAL DISCLOSURE BULLETING vol. 27, no. 5, October 1984, page 3164 XP 002066860, and in WO-A-89 09392. Reference is also made to U.S. Pat. No. 6,011,478 (Suzuki et al).
The invention aims to improve the sensitivity of such a detector and such a method so that the detector and the method are better able to discriminate against particles of a type which are not intended to be detected.
According to the invention, therefore, the detector as first set forth above is characterised in that the radiation of the other wavelength is infra-red radiation, and by output means for comparing outputs from the detecting means respectively corresponding to the received and detected radiation between about 400 nm and 500 nm and the received and detected infra-red radiation whereby to produce a warning signal when the comparison indicates that the particles are of a predetermined type but not when the comparison indicates otherwise. Similarly, according to the invention the method as first set forth above is characterised in that the other wavelength is a wavelength of infra-red radiation, and by the step of comparing two outputs respectively corresponding to the received and detected radiation between about 400 nm and about 500 nm and the received and detected infra-red radiation whereby to produce a warning signal when the comparison indicates that the particles are of a predetermined type but not when the comparison indicates otherwise.